1. Field of the Invention
The present invention relates to a seat belt retractor, and more particularly to a seat belt retractor that is provided with an electric actuator and a pyrotechnic pretensioner.
2. Related Technology
In conventional seat belt retractors, a spindle is caused to rotate in a winding direction, by a motor, when a sensor detects a sudden deceleration state of a vehicle. In a case where a collision is possible, the seat belt (webbing) is wound by a predetermined amount, to restrain lightly thereby an occupant, and during a collision, the pyrotechnic pretensioner is operated, the seat belt is wound forcibly, and the occupant is held reliably. (See, for instance, Japanese Patent Application Publication No. 2002-326558, discussed below.)
Upon operation of a pyrotechnic pretensioner in the seat belt retractor disclosed in Japanese Patent Application Publication No. 2002-326558, engagement between a final gear and a pawl is released through reverse rotation of a motor in a power transmission mechanism that transmits power from an electric actuator to a spindle; power transmission from the motor to the spindle is thus broken off, and the spindle is prevented from receiving the load of the motor upon winding of the seat belt by the pretensioner.
In another seat belt retractor, engagement between a final gear and a pawl is released through reverse rotation of a motor upon operation of a pyrotechnic pretensioner. In such a configuration, where the engagement between a pawl and a final gear is released by a motor, an accurate disengagement operation may fail to take place accompanying a sudden collision or the like. Also, some time may elapse from start-up of the motor until the release operation is performed. Moreover, no consideration has been given to the attitude of the pawl after release.